The manufacture of semiconductor devices typically includes a photolithographic process. Photolithography typically involves various combinations of material deposition, etching, and chemical treatment.
A portion of a typical lithography process would proceed as follows. A film (e.g., a metal film) layer is deposited on a substrate. The film layer is typically only a few nanometers (nm) thick. A photoresist layer is then deposited on the substrate (i.e., over the film layer). A photoresist is a photosensitive material that hardens when exposed to light. The positive or negative photoresist may typically be spun on to the substrate and may include solvents to ensure a uniform coating. Such photoresists may be soft baked after deposition to drive off excess solvents. The photoresist is then selectively hardened by exposure to light in specific places. Typically a mask (i.e., a transparent plate having a printed pattern) and a light source (scanner or stepper) are used to illuminate the specified portions of the photoresist layer. Then, the non-exposed portion of the photoresist layer (e.g. the non-hardened portion of the photoresist layer), is removed by the photoresist developer. The underlying portion of the film layer (i.e., metal, oxide, nitride, etc.) is etched using a chemical treatment (wet etch) or plasma (dry etch). Subsequently, the exposed portion of the photoresist layer, is developed leaving the patterned film layer, which can be used to etch the underlying material, or be used as a mold for plating or deposition of material to fill in the pattern to complete the image transfer from patterned photoresist to the patterned material needed for the actual device layer.
FIG. 1 illustrates a typical apparatus and method for applying photoresist to a wafer in accordance with the prior art. System 100, shown in FIG. 1, includes a wafer platform 105 on which a wafer 106 is placed. Photoresist is dispensed from photoresist nozzle 110 and applied to wafer 106. The wafer platform 105 and wafer 106 are then lowered into the chamber (bowl) 120, as indicated by arrow 121. The motor 130 then rotates the wafer spindle 131 to spin the wafer platform 105 and wafer 106. Spinning the wafer helps to dispense the photoresist across the wafer and level the photoresist. Upon initial spinning, a large proportion of the photoresist is spun off the wafer against the inner surface of the bowl. This excess photoresist proceeds down drainpipe 135 to receptacle 140 or may proceed to a waste drain.
A solvent is directed toward the edge of the wafer to effect edge-bead removal, which is the removal of photoresist from the edge of the wafer. This solvent is dispensed through edge-bead removal nozzle 145. The solvent, and any particulate matter from the edge-bead removal process, also proceeds down drainpipe 135 to receptacle 140.
To prevent excess photoresist from accumulating on the inner surface of the bowl, the bowl is rinsed with a solvent. Typically, the same type of solvent used for the edge-bead removal process may be used for the bowl wash. The solvent is dispensed along the inner surface of the bowl, through, for example, a weeping seal 150, as shown in FIG. 1. Again, the solvent from the bowl wash proceeds down drainpipe 135 to receptacle 140.
The excess photoresist in receptacle 140 is contaminated with solvents and particulate matter and cannot be reused for photolithography. This photoresist is expensive and adds significantly to the cost of semiconductor device manufacture. Moreover, there is a significant cost associated with disposal of the photoresist/solvent byproduct.
Previous efforts to address this situation have focused on reducing the amount of photoresist used. For example, over the past twenty years, increasingly accurate pumps to dispense the photoresist have been developed. Through the use of such accurate pumps, the amount of photoresist used has been reduced dramatically. Still, the photoresist that is used is used inefficiently, a large proportion of the photoresist is discarded, with the attendant costs and disadvantages.